Thanks to all for some very good information. Occasionally resurrecting a venerable thread is a very good idea.
Looking at Mark's squimp and Boot's "this guy", a major difference I noticed is the orientation of the fly. Boot's faces the line and rod, Mark's faces away. So on a retrieve, Marks moves butt in front, Boot's face in front. Which way does a shrimp move through the water? Probably doesn't matter that much, just curious.

Oh man, the orientation of shrimp patterns always leave me scratching my head (and some have eyes at both ends???)

I definitely think there's more evolution to come in fly design for Puget Sound. Watch us eventually copy and apply all the tropical patterns. Ive caught multiple species on a chartreuse Crazy Charlie, and WadinBoot's This Guy looks much like that to me. I should try a Borski Slider. And I think crab patterns for the sound have been mostly ignored.

Boot's faces the line and rod, Mark's faces away. So on a retrieve, Marks moves butt in front, Boot's face in front. Which way does a shrimp move through the water? Probably doesn't matter that much, just curious.

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If you watch a shrimp up close they feed by scampering around on their legs, they move mainly anteriorly or side to side, dependent on the reach of their antennae. They are sorta slow and deliberate when feeding. When they are threatened they curl their tail up and shoot backwards, really quickly, curling and uncurling their tails, they move erratically. The difference of my pattern, I guess, is these shrimp are sorta floating, I dead drift the pattern, I don't think they are feeding so much as hauling ass off down tide to deeper realms. They are expending minimal energy out of the estuary to the deeper sound waters. Often with what looks like a bunch of eggs tucked up by their legs

The part of the puzzle I don't get here is when or if the shrimps migrate BACK, and if so where do they hang- in the eelgrass? If I could figure that out that's going to be another month or so of fun fishing.

Hmmm... a young bait slinger I know was jig/float fishing for hatchery summer runs last July/Aug, and his bait of choice was purple coon striped shrimp. They apparently out-fished sand shrimp enough so that he would pay for the coon stripes even though he could just go pump out sand shrimp for free.

If you watch a shrimp up close they feed by scampering around on their legs, they move mainly anteriorly or side to side, dependent on the reach of their antennae. They are sorta slow and deliberate when feeding. When they are threatened they curl their tail up and shoot backwards, really quickly, curling and uncurling their tails, they move erratically. The difference of my pattern, I guess, is these shrimp are sorta floating, I dead drift the pattern, I don't think they are feeding so much as hauling ass off down tide to deeper realms. They are expending minimal energy out of the estuary to the deeper sound waters. Often with what looks like a bunch of eggs tucked up by their legs

The part of the puzzle I don't get here is when or if the shrimps migrate BACK, and if so where do they hang- in the eelgrass? If I could figure that out that's going to be another month or so of fun fishing.

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There are four different groups of shrimp-like creatures that are potential fish food in the PNW. They are a) thallasinid decapod (10 walking legs) shrimps, b) caridian decapod shrimps, c) paracarid mysid shrimp, and d) uphausiid shrimp. The last two categories are probably more important food sources for cutthroat trout or silver salmon (see http://docs.streamnetlibrary.org/CoastalCutthroatData/sn600219.pdf).

A) The Thassinidae include blue mud shrimp (Upogebia pugettensis) and bay ghost shrimp (Neotrypaea = Callianassa californiensis). Both species spend most of their lives in densely-packed mounded burrows on mud and sand areas of the intertidal and nearshore subtidal. They are not powerful swimmers or demonstrate a strong escape kick. I'm not sure how accessible they are normally to salmonids but they may leave their burrows every once in a while to explore new opportunities, especially when small. Females retain eggs on their abdomen until late in the larval stage before the young hatch as late stage larvae and spend some time in the plankton. The burrowing activities of these species are the bane of oyster farmers because they kick up sediment which bury oysters or undermines them. They are harvested by sucking them out of their tubes and can survive out of water if refrigerated. You will often see them in bait stores.

B) Classic shrimp, the Caridian decapod shrimp, include pandalids (genera Pandalus and Pandalopsis, such as spot prawns and dock shrimp), Heptacarpus (several species), and crangonids (Lissocrangon stylirostris - smooth bay shrimp and Crangon nigricauda). These are primarily benthic omnovores, walking around on the bottom when they forage. All three have well-developed tail escape responses. The heptacarpid species are cryptic, blending in with the algae and rocks in their environment. The crangonids bury themselves in the top layers of sand. They can be dislodged by wave action and have to rebury themselves. Like the other decapod crustaceans in group A, they reproduce once per year (generally late spring / early summer) and females hold the eggs on their swimming legs (pleopods) along the abdomen until the young reach the late larval stage when they hatch out of their eggs and head into the plankton. I'm not sure about the Heptacarpus and crangonids, but the Pandalus shrimps change sex. They are males for the first year and then change sex to females for year two and as long as they live thereafter, a phenomenon known as protandrous hermaphrodites.

C) The mysid (see https://en.wikipedia.org/wiki/Mysida) "shrimps" = opossum shrimp are small, typically half to an inch long at best and most are translucent. The freshwater shrimp Mysis diluviana so important in some tailwater fisheries belong to this group too. Most of our many species of mysid shrimps form dense schools near surfaces, such as kelp forests or eel-grass beds. A few species form schools in open water and deep water. At least one species (Archeomysis grebnitzkii) burrows in sandy beaches right at the tide line. They swim by beating their legs (which may also set up feeding currents for feeding on plankton) but can escape with a quick tail flip. Like other peracarid crustaceans (which include amphipods (scuds) and isopods (pill bugs)), the females retain their eggs in a brood punch (marsupium) on the ventral side of their thorax. The fertilized eggs complete their development in the pouch and the young emerge as miniature adults (no larval stage). Individuals can breed several times per year, allowing for explosive population growth. In my experience, mysids are very abundant in nearshore waters and are likely to be major food items of salmonids. Distinguishing mysid remains from the better-known decapod shrimps in fish gut contents can be problematic and the two are often lumped together.

D) Euphausiid shrimps = krill (see https://en.wikipedia.org/wiki/Krill) are pelagic and translucent, often with red spots on the ventral surfaces of the body. While most are less than an inch long, there are species that are several inches long. They use their legs to set up filter feeding currents to draw phytoplankton initially but often graduating to zooplankton. When threatened, they will use a tail-flip response to attempt escape. Most species are bioluminescent, possibly as countershading against predators from below. While females of some euphausiid species do retain their fertilized eggs as an attached egg sac, most species release their eggs as soon as they are fertilized. During my many years in the San Juan Islands, I generally saw euphausiids in open water, typically at night, especially after big tides. I think that euphausiids are typically much deeper than mysids unless strong currents have drawn euphausiid schools up to the surface.

How much does this matter to flyfishers in the PNW? Most of our "shrimp" patterns are probably fine mimics for mysids and euphausiids. A slow steady retrieve will mimic more typical feeding movements. A series of fast strips mimic tail-flips to avoid predators. [Interestingly, in some of my research on sculpins feeding on shrimp, a shrimp in the middle of a tail flip appears to be far more vulnerable to capture than a shrimp that had not yet tail-flipped. My hypothesis for this difference is that the direction and velocity of a shrimp that has not yet tail-flipped is unpredictable to the sculpin but the direction and speed of a shrimp that has tail-flipped in predictable and can be anticipated.]

Yes, thanks for all that eddycation, Cabezon! I suspected that a pale tan, translucent shrimp that flipped into my boat when being chased by a cutthroat while I was fishing a tidal creek (just below the head of tidewater) was some kind of mysid. It was maybe an inch and a half long, and nearly transparent. While I was looking at it in the palm of my hand, it clicked out and again made its escape!